Short wave receiver



D. GRIMES SHORT ,WAVE RECEIVER July 2, 1935.

Filed June l2, 1951 AIIIIIIII INVENTOR DAVID GRIMES ATTORN EY Patented July 2, 1935 UNITED STATES FFI CE snoer WAVE Recouvrirv David Grimes, Don'gan Hills, Staten Island, N. Y.,

assignorto RadiofCorpol-ation of America., a." corporation of DelawareV 'i Application June 12 1931sSeriaLl Vs ammi.` (C1. 25o-27)-V My present invention relates to radio receivers, and more particularly to short Wave radio Ieceivers adapted to be powered from alternating current sources.

1t is one of the main objects of my present invention to provide in'a short wave radio receiver,A a novel and highly improved method of securing regeneration in the detectorv stage oompris'ing an electron discharge tube of the screen IU grid type. v

Another important object of the present invention is to provide in a short Wave radio receiver employing a screen grid detector a novel and highly efficient arrangement for controlling f5 regeneration, the arrangement comprising a variable impedance for regulatingthe potential ap. plied to the screen of the detector tube. Another object of the presentinvention is to provide in a short Wave radio receiver avstage of tuned radio frequency amplication employ ing a screen grid tube, and a succeeding .detector stage havin-Cf a tunable input circuit, a common means for transferring energy from the output Circuit of the amplifier tube to the said tunable input circuit of the detector stage and siml taneously transferring energy from the output circuit of the detector stage to its tunable input circuit, Y t

Still another object of the present invention is to provide a short wave receiver adapted for use in connection with signals having Wavelengths below one hundred meters, said receiver being arranged for energization of its circuits from an alternating current source employing a-rectifer,

tiiier to suppress such harmonics of the fundamental frequincy of said energizing source Whoh are discernible by the detector ofthe .short Wave receiver.

And still another object of the present invern` tion is to provide for use with a Shortwave receiver employing a screen grid detector utilizing regeneration control means in the screen circuit, an arrangement for energizing the circuits of said receiver from an alternating current powel` line source, said arrangement including a double Wave rectier circuit anda Succeeding lter oil"-A cuit, there being buier capacities utilized inthe anode .circuits of the rectier to, suppress ultrahighharmonicsof the fundamental frequency of said source.

VStill-other objects of the present invention are of short wave radio receivers, andto particularl ,provide a short wave radio receiver, adapted-for additional means being associated with saidrec` operation with wavelengths substantially below a hundred meters whichis not only reliable in operation', but economically manufactured and assembled.Y .a y

The novel 4features whichl believe to be chars 5 acteristic of my invention`- are set forth in par-f ticular-ity in the appended claims, the invention itself, however, as to both its organization and method of operation'willbest be understood by reference to the following description taken in connection withthe drawing in which I have in! dicated diagrammatically one circuit organiza? tion whereby'm'y invention may be carried into effect, .7 7 -Y 1n thedrawing,A 1 s Fig. 1 diagrammatcally shows a circuit embodyir the vpresent invention, i 2 isa graphical representation of operation of the harmonic suppressingV means used inconnection :with the power rectifier.

Referring to the accompanying drawing there showninFg. 1 in purely diagrammaticv fashf ion, an ,arrangement forreceiving short waves Within a wave length range .ofthe order of 15 to v meters inclusive. Thereceiver, in Fig. l, comprises any well known type of signal energy collecting such as agrounded antenna circuit A, G. The collecting means is coupled, as at Y M, to the input circuit of a stage of tunedradio frequency amplificatonwhich includes a screen grid tube I.A The input electrodes of .the tube are connected to a re'Sonant circuit including a va riable condenser .2 adapted to tune the radio frequency amplification stage to the desired short wave frequency. y l

VThe cathode of the tube I includes the usual gridfbasing resistor 3 having a value of about 450 ohms. The resistor is shunted by a radio frequency by-pass condenser 4 having a value of about 0.6 microffarads. The screen circuit of the tubeincludes a resistor 5, having a value of about 145.0 ohms, a radio frequency by-pass ca.- pacitysyof'aboutlthesamemagmtude as the ca.

pacity I, ,it being connected between the positive leg of thecathode and .the screen element. Y

A f tblifzlillll 'lfprovidespositive Y potentiarfor the screen velement of tube I, the conductor 'l being .connected to an appropriate tap 8 on any well knowntype of, voltage divider resistor 9 disposed in the power supply circuit. It Will be noted that the .conductor 1 vis connectedrtoA a point on the resistor 9 such that a potential of 90 volts is appliedto the screen element` of i tube I. kThe anodeV of the .screen grid tgube lI has potential applied, to a path which includes;

- Y coupled with meson Vls 'disposedl inthe input circuit of the detector stage of the receiver, the detector stage including Vascreen YVgrid tube I1. ff. A

variable condenser I8 is utilizedfor uning the resonant input circuit of the detector age tothe same frequency toA which the inputcircuitvof the#y amplifier tube I has been tuned.f The usual seriescapacity I9 and grid leak resistor 20 areprovided in the grid circuit of tube I1 to provid@ @etere-, tion. The screen element ofthe tube I1 is Vco'n-v nected through conductors 2| and 22,!1in series.'

withY the inductance coil II, therebeing a fixed capacity 23, of about 0.01 microfarads disposed in Vseries in the'con'ductor 22.'

f* 'Potential iS applied to the screen eiefuet of tube. I1 through a path which includes'ftlie con ductor 2|, a xed resistor' 24,' Ahaving a magnitude of about 30,000 ohms, the variable "contact member 25, a resistor 26 having avalue'of about l 50,000 ohms, and the conductor 21, it "being noted that one terminalof the resistor 26 is grounded. The conductor 21 is connected to a tap 28on the Vvoltage dividers` such thatl a potential of 45 `volts and Yto permit definite and reproducible logging.V

canbe applied to the screen element of detector tube .si Y l L 1 The` anode of Vthe detector tube has potential applied to it through a path which includes a coil 29, "a resistor. 30 having afvalue-` of about 0.1 megohms, .conductor 3|.' and conductorj', the latter vconductor being connected toltap Il'to provide a potential of abouti135j volts.V 'A radio frequency byfpass capacity $2 having a'valueof about 0.00015 micro-farads is connected Vl'letween thelscre'en element and anoderoftubev I1; 'The' output of detector tube Il isimpre'ssed upon the input of any well known type ofaudio frequency amplienwthrougha conductor'33; and acondllctor 34. i' 'i r'L-'The'audio frequency amplifiercarrltye` of any type well known to those skilled in the'iart, and for example, Vmayinclude one, or more, stages y o f audio frequency amplification embodying; single tubes,`and a final power amplifier embodying a push pull stage. However, since the amplifier does not compriseV the present invention, 4'it need not be described in any furtherl detaihjexcept to point out that the output of the audiovfrequen'cy amplifier may be utilized in any wellknown inanner, asjby a loud speaker, or head L Jhones,V orany ,other desired audible,` and 'even visual, repro,- Vducen .l 'The coil II has a dual `)function accordirs'ii the present invention. fIt serves-fto'tranlsffer ain# plied signalV energy from .'Vtheanode circuit 'of the jscreen` grid'y tube VI t`o 'the resonant input;

, ysecured,'and these; coils arepreferably linter-v Y wound ,to piuvidthis optimum ppnuinun.:

'-l'I'h'efceil I I, also, compisesa fedlack path for energy transferred vfrom the anode circuit @of the detector tube I1 tothe input .circuito'f lthe tube.

Ir'iother words-the detector stage is regenerative, the regeneration being secured through la path which includes the con H. "It wi11, therefore-be seen that the latter functions as the primary coil of interstage transformer and simultaneously as a feed-back coil in a regenerative detector stage.

According to the present invention, regeneration in the detector stage is regulated in a novel manner, the regulation ,being securedV by means Y kof a variable impedance in the screen circuit of'v rthe detector tube I1.

vices,rwell known to those skilled in the prior art,VVV

Instead of employing dedisposed in the anode circuit of the detector tube,

A'the present invention utilizes the action of the zscreen element to control regeneration. That isto say, the potential applied to the'screen elementof tube' I1 is controlled by means of the variable -resistor comprising the variable contact and the resistor 26. Y A,

,By varying the position of the contact member- `25 with respect to the resistor 26 reliable and sat-` isfactory Ycontrol Vof regeneration is secured.k

While it is not desired to limit the present inzoV vention to any particular theory, the following explanation'is given to make clear the manner in which the variable impedance inthe' screen, circuit controls regeneration of thedetect'or stage;

Regulation' by the conventionalvariable tickler method carmot be used Ybecausechanging the spacingl of the'vtickler, changesthe associated v tuning condenser I8 setting excessively at short waves. Hence, the present arrangement is necessary to insure uni-control between the condensers 2and I8, as well as to promote facility in tuning,

Bygufsing'afixed tickler, the regeneration is contolled by Vchanging theV gain Von the'tube IIT by varying the'screenvoltage as described above, through a path including condenser 3,2, lead ZI,

Vcondenser 423, Vlead 22,r fixed tickler` I I,fixed condenser I5 to ground.-V Condenser 32 has been addedy toaugment the self-capacity, ofthe tube existingbetweenplate and screen. "This increases thelregenerative action immensely. Choke- 29 confines the radio frequency energy to its proper, Y path;l l Y vTIrifadapting the present short wave receiver for usein connection with an alternating current Since the arrangement is vWell known to those Y skilled in the art, only the connection between thevanodels of therectifler and thepowersupply circuit are shown. 'Ihe mid-point 38,"01'v the 39 to the groundedV terminal of the voltage divider 9, While one` side of thecathode, of the rectifier .35i is connected through a conductorV 40 tothe Vhighpoteritial terminal oftheV voltage divider 9. The usual filter ycircuit comprising a plurality ur. siintiapacities 4|, audseries cholgesz are utilized to suppress the relatively low harmonics offhthefundamental frequency of the source SV."

is Vpower line s'ource,a double wave rectifier-35 is 'secondary`36, is'lconnected through a conductor Merely byway of illustration, andnotby way 0f Y limitation, it is pointed out that the filter ca-V Dacity adjacent tothe rectii'ler'm'a'y havev a value of 2 micro-farads, while the succeeding ca.-

paclties 4I' mayV each have a ,value'of 3 microfarads, while eachpof the capacities 42 following the last capacity 4I', may have a value of about 1 micro-farad.Y

` Furthermore, each choke 42 mayy have a value of about 1000 ohms and henries at 100 mils drain. Anode potentials for the audio frequency amplifier tubes may be taken oif from point 43, and the high potential terminal of the voltage dividei` 9. Illustrative values of such potentials are given as 250 volts, it being understood that potential is utilized usually-for the power amplier tube, and 180 volts to be utilized on t'ne earlier audio frequency amplifier tubes. However, it is believed that these arrangements are so Well known that they need not be described in any further detail.

In Fig. 2 there is graphically shown the operation of the double wave rectifier. As is well known to those skilled in the art, the rectifier 35 functions to convert the alternating wave form into a pulsating uni-directional wave form. For the purpose of explanation alternate half cycles are shown in full lines, while half cycles between the full line half cycles are shown in dotted lines. It was found, by actual experience, that when the short wave receiver disclosed herein was utilized with a power supply circuit as described herein, that due to the sharp cut-off action at each half. cycle, hum frequencies were introduced, and detected by the short wave receiver, which frequencies corresponded to ultra-high harmonics of the fundamental frequency of source S.

It can be mathematically demonstrated that the sharp cut-off inherent in a single wave or double wave rectifier action, gives rise to a series of harmonics of the fundamental frequency of the source S. It was found that when a short wave receiver employing a regenerative detector, sufficiently sensitive to detect frequencies corresponding to a range between 15 to 100 meters, was utilized, that ultra-high harmonics produced by the sharp cut-off action of the power rectifier were detected by the regenerative detector, and made discernable. This resulted in annoying hums, and other audible sounds. It should be. noted that when the regenerative detector is tuned to its maximum wave length of 100 meters, its detecting signals have a frequency of 3,000,000 cycles. Accordingly, it can be readily seen that the harmonics of the fundamental frequency of source S which would become discernible when the receiver is tuned to 3,000,000 cycles, would have to be of the order of magnitude of at least 50,000.

The usual filtering means employed in power supply circuits can not be employed to suppress the ultra-high harmonics having magnitudes as high as 50,000. Accordingly, it was realized that since these extremely high harmonics arose because of the sharp cut-off action of the rectifier, an arrangement which would change the sharp cut-off action of the rectifier to a gradual slope would eliminate to a very great extent these extremely high harmonics. This change in rectifier action is simply and efficiently secured by disposing a buffer condenser 50 between each anode of the rectier 35 and ground.

The value of each of these buffer condensers is preferably 0.01 micro-farads. When buffer condensers are employed, as shown in Fig. 1, in con- Y nection with the anodes of the rectifier tube, there is secured a gradual slope in the cut-off between alternate half cycles. This is shown in Fig. 2 by the reference numeral 5I. It will, therefore, be seen that by employing buffer condensers from the anodes of the double wave rectifier to ground,.hum frequencies about 3,000,000 cycles are effectively eliminated, and that this is secured by changing the sharp cut-olf action of the rectifier to a gradual slope.

While I have indicated and described one arrangement for carrying my invention into effect, it will be apparentto one skilled inV the art that my invention is byno means limited .to theV particular organization shown ,and described, but that many modifications may be made Without departing from thev scope of my invention as set forth in the appended claims.

What I claim is:

1. A regenerative circuit comprising a space discharge device provided with anode, cathode and grid electrodes having external connections for forming input and output circuits for said device, a screen element in said device, a source of positive potential connectedto said screen element, a path between the output and input circuits for feeding energy from the output to the input in regenerative phase, and means comprising a, screen potential varying means associated with said screen element for determining the extent of the regenerative feed-back through said path.

2, In combination, a circuit including an electron discharge tube of the screen grid type having input and output circuits, a current source for energizing said tube and a tapered impedance shunted across said source at least a portion of which is included in said output circuit, a feedback circuit for transferring energy from said output circuit to said input circuit, a resistance shunted across at leastr a portion of said impedance, a circuitV including at least one reactive element connected between the screen element and cathode of said tube and means for variably connecting a point of said last named circuit to said shunt-ing resistance for varying Within predetermined limits the potential impressed upon the screen element relative to the cathode of said. tube and thereby control the transfer of energy through said feedback circuit.

3. In a. regeneratively connected screenV grid thermionic tube circuit the step in the method of controlling the degree of regeneration which comprises varying the potential applied to the screen element of Athe tube and thereby changing the amplifying characteristics of the tube whereby the flow of energy from the output to the input thereof is controlled.

DAVID GRIMES. 

